In order to impart to a coated film self-cleaning function such as antifouling property or easy washing property, it is common to add to a coating composition a stain-proofing agent capable of imparting hydrophilicity and oil repellency to the surface of the coated film. Further, in view of environmental aspect, it has been desired to realize the self-cleaning function with an aqueous coating material having a low content of organic solvents.
The following have been proposed as an aqueous coating composition containing a stain-proofing agent for an aqueous coating material.
(1) An aqueous coating composition comprising a synthetic resin emulsion and an alkoxysilane modified condensate as a stain-proofing agent for an aqueous coating material (Patent Document 1).
(2) An aqueous coating composition comprising an aqueous synthetic resin dispersion and as a stain-proofing agent for an aqueous coating material, a fluorinated copolymer having (meth)acrylate units having a C1-6 perfluoroalkyl group, (meth)acrylate units having a poly(alkylene oxide) chain, and (meth)acrylate units having a dialkylamino group (Patent Document 2).
However, the aqueous coating composition (1) contains an alkoxysilane modified condensate having a relatively high reactivity, and is thereby problematic in the storage stability.
The aqueous coating composition (2) has favorable storage stability, however, in a case where it contains an aqueous fluorinated resin dispersion as the aqueous synthetic resin dispersion, the fluorinated copolymer as the stain-proofing agent is less likely to migrate to the surface layer of the coated film, and the self-cleaning function may not sufficiently be imparted. Particularly if it contains an isocyanate compound as a curing agent, the fluorinated copolymer reacts with the isocyanate compound in the process of migrating to the surface layer of the coated film, and the fluorinated copolymer is still less likely to migrate to the surface layer of the coated film.